The extension is for three years and is worth $12.3 million, averaging $4.1 million per year, a source told ESPN.com.

Mason was slated to become a restricted free agent July 1.

The 25-year-old Mason is 19-11-5 with a 2.48 goals-against average and .917 save percentage entering Philadelphia's game against the New York Islanders on Saturday night. Mason was acquired from Columbus last April, and has become the team's No. 1 goalie.

Mason played well despite the team's poor start and has helped the Flyers into playoff contention. The Flyers are 23-12-5 since a 1-7 start.

Mason was the NHL's Rookie of the Year in 2008-09 when he was 33-20-7 for the Blue Jackets.